Wow. With "secondhand embarrassment" you have deftly labeled a feeling I have had so many times in my life but have never been able to succinctly name.
I wonder if it's similar to how some phising emails will contain intentional grammar and spelling errors. I've been told that this works as a filter, since savvy people will be put off by such things leaving only the easy targets.
Or was it the credentials of "I bought $12 of Bitcoin when I was young and it increased in value" that didn't sell you?
It seems like a slam dunk from over here, so I'm confused as to what you didn't find convincing....